Even Doctors May Have Trouble "Doing the Math"

February 15, 2008

University of Cambridge researchers report that (British) doctors may have to brush up on their mathematics, especially when it comes to converting from a ratio to milligrams per milliliter. Apparently trying to do that kind of math "Leads to muddles between hundredths and thousandths, said Daniel W. Wheeler, an anesthesiologist and a clinical lecturer at the university. “And errors tend to be by factors of 10—large and potentially dangerous, he said.

The researchers had come to those conclusions by evaluating the math skills of a group of 28 doctors who were told that a 5-year-old patient was having an allergic reaction to peanuts, which might be fatal. Emergency treatment involved a quick injection of 0.12 milligrams of epinephrine.

Half the doctors were given bottles of epinephrine labeled "1 milligram in 1 milliliter solution" and half were handed bottles labeled "1 milliliter of a 1:1000 solution." Both groups, of course, had the same amounts of medication. In the first group, however, it was expressed as a ratio; in the second as a concentration.

It turned out that 11 of the 14 doctors in the second group, but only two in the ratio group, calculated the correct dosage quickly enough. The group of doctors who held the medication expressed as a concentration needed an average of only 35.5 seconds before they were ready to inject the patent. The ratio group averaged more than two minutes. To make matters worse, one of these doctors was ready to administer one milligram of epinephrine, which is about eight times too much!

The researchers' article "The Effect of Drug Concentration Expression on Epinephrine Dosing Errors" appeared in The Annals of Internal Medicine (January 1, 2008).

Source: New York Times